High-bandwidth digital content protection (HDCP) is a specified method developed by Digital Content Protection, LLC, for protecting copyrighted digital content that uses an interface such as Digital Video Interface (DVI). FIGS. 1 and 2 illustrate basic examples of HDCP systems. In FIG. 2, the HDCP system 200 encrypts the digital content transmission between a video source 204 (set-top box, computer, DVD, etc.) and a receiver or display 206 (Liquid Crystal Display, television, etc.) via DVI 202.
FIG. 1 illustrates an HDCP System 100 wherein two or more HDCP Devices are interconnected through an HDCP-protected Interface 113. The Audiovisual Content protected by HDCP, HDCP Content 102, flows from an Upstream Content Control Function 110 into the HDCP System 100 at the most upstream Transmitter 112. From there, the HDCP Content 102, encrypted by the HDCP System 100, flows through a tree-shaped topology of HDCP Receivers 114 over HDCP-protected Interfaces 113. HDCP Receivers may be HDCP Repeaters 116 that serve as downstream HDCP Transmitters emitting the HDCP Content 102 further downstream to one or more additional HDCP Receivers 118.
HDCP is sometimes required to be enabled if a DVI display is used. However, that requirement degrades the performance of the digital content 102, particularly during a rapid channel change process (surfing). HDCP authentication is dependent on video attributes such as resolution and aspect ratio. Since channel changes result in new video attributes and potentially new resolutions such as the ATSC resolution standards 480p, 720p and 1080i, and aspect ratios, such as 4×3 (full-screen) or 16×9 (wide-screen), among others, there is a need for HDCP re-authentication for each channel change.
HDCP is designed to protect the transmission of Audiovisual Content 102 between an HDCP Transmitter 112 and an HDCP Receiver 114. The system also allows for HDCP Repeaters 116 that support Downstream HDCP-protected Interface Ports 120. There are three facets of the content protection system. First, there is the authentication protocol, through which the HDCP Transmitter verifies that a given HDCP Receiver is licensed to receive HDCP Content. With the legitimacy of the HDCP Receiver determined, encrypted HDCP Content is transmitted between the two devices based on shared secrets established during the authentication protocol. The use of such shared secrets prevents eavesdropping devices from utilizing the content. Finally, in the event that legitimate devices are compromised to permit unauthorized use of HDCP Content, renewability allows a HDCP Transmitter to identify such compromised devices and prevent the transmission of HDCP Content.
The HDCP Authentication protocol is an exchange between an HDCP Transmitter and an HDCP Receiver that affirms to the HDCP Transmitter that the HDCP Receiver is authorized to receive HDCP Content. That affirmation is in the form of the HDCP Receiver demonstrating knowledge of a set of secret device keys 208. Each HDCP Device is provided with a unique set of secret device keys, referred to as the Device Private Keys, from Digital Content Protection, LLC. The communication exchange, which allows for the receiver to demonstrate knowledge of such secret device keys 208, also provides for both HDCP Devices to generate a shared secret value that cannot be determined by eavesdropping on that exchange. By having that shared secret information embedded into the demonstration of authorization, the shared secret can then be used as a symmetric key to encrypt HDCP Content intended only for the Authorized Device. Thus, a communication path is established between the HDCP Transmitter and HDCP Receiver that only Authorized Devices can access.
Thus, a heretofore, un-addressed need exists in the industry to address the aforementioned HDCP re-authentication process for each channel change.